The present invention relates to a pressure sensor and data input apparatus which are capable of inputting operation information and which are suited for application to performance information input apparatus for inputting performance information.
FIG. 25 is a sectional view showing an example of a pressure sensor employed in a conventionally-known electronic percussion instrument, which is disclosed, for example, in Japanese Patent Publication No. 2944042. The pressure sensor 200 shown in FIG. 25 includes a lowermost layer in the form of an insulator 210, such as an insulating film, formed in a circular shape. Resistance surface 211 of a circular shape, formed for example of carbon, is attached to the upper surface of the insulator 210. Annular or ting-shaped electrode 213 is provided on and along the circumference of the resistance surface 211, and another electrode 212 is provided at the center of the resistance surface 211. Further, a pressure-sensitive resistance element 215 is provided over the resistance surface 211 with a predetermined space interposed therebetween. To provide such a predetermined space, an annular spacer 214 is interposed between the resistance surface 211 and the pressure-sensitive resistance element 215. Electrode 216 of a circular shape is attached to the upper surface of the pressure-sensitive resistance element 215. Further, a circular striking surface 217 formed of a flexible film is attached to the upper surface of the electrode 216. As the striking surface 217 of the pressure sensor 200 constructed in the aforementioned manner is struck with a stick, positions of the striking surface 217, electrode 216 and pressure-sensitive resistance element 215, corresponding to the struck position, flex so that the pressure-sensitive resistance element 215 contacts the resistance surface 211.
FIG. 26 shows an equivalent circuit among the electrodes 212, 213 and 216, where R1 represents a resistance value of the pressure-sensitive resistance element 215. Further, R2 and R3 represent resistance values of the resistance surface 211. Contact d between the resistance value R2 and the resistance value R3 is a struck position where the pressure sensitive resistance element 215 flexes to contact the resistance surface 211. Namely, the resistance value R1 of the pressure sensitive resistance element 215 varies in accordance with a striking intensity of a stick, and a ratio between the resistance values R2 and R3 between the electrodes 212 and 213 varies in accordance with the struck position. In order to detect variations of these resistance values R1, R2 and R3, the electrodes 212, 213 and 216 are connected to intensity/position separation circuitry 220. In the intensity/position separation circuitry 220, resistances of a fixed resistance value are connected to the electrodes 212 and 213 to construct a bridge circuit, and a constant current supply is connected between the bridge circuit and the electrode 216. Thus, the struck position is detected by measuring a voltage across the electrode 213, and the striking intensity is detected by measuring a voltage between the bridge circuit and the electrode 216.
Then, a not-shown tone generator is controlled, on the basis of information of the detected striking intensity and struck position, to generate a tone corresponding to the striking intensity and struck position. The thus-generated tone is amplified and audibly sounded through a speaker.
However, with the conventionally-known pressure sensor for inputting performance information through resistance change, detecting accuracy of the struck position can not be enhanced because it is not easy to make the resistance surface 211 of a uniform electric conductivity. Further, because it takes a considerable time to detect, from voltage values of the plurality of electrodes, performance information comprising information of a striking intensity and struck position, which would thereby lead to a slow speed of response. Therefore, when the striking surface 217 is repetitively struck with the stick at high speed, the detecting capability of the pressure sensor 200 may not be able to appropriately follow the high-speed striking. Further, because an expensive pressure-sensitive resistance element 215 having a great area is required, the necessary manufacturing cost would increase. Furthermore, the conventional pressure sensor 200 is unable to appropriately respond or behave when striking forces are simultaneously applied to two or more positions of the striking surface 217.
Pressure sensor using capacitance change, in place of resistance value change, for performance information input is also conceivable. Such a pressure sensor using capacitance change (i.e., capacitance-change-based pressure sensor) can dispense with the resistance surface and pressure-sensitive resistance element. Further, the capacitance-based pressure differs in principle from the conventional pressure sensor using resistance change (i.e., resistance-change-based pressure sensor) in terms of the manner in which information of a striking intensity and struck position is detected, and thus, it can avoid the inconveniences of the conventional pressure sensor. Note that the capacitance used by the capacitance-change-based pressure sensor is one produced through opposed electrodes; namely, the capacitance changes due to change of a space between the opposed electrodes in response to input of performance information. However, such a capacitance-change-based pressure sensor tends to be unavoidably susceptible to an external disturbance because the capacitance changes as part of a human body, metal or the like approaches the electrodes. Therefore, the capacitance-change-based pressure sensor must be kept at a relatively low sensitivity. Besides, with the capacitance-change-based pressure sensor, where the capacitance change does not differ between different struck positions, it is difficult to detect different struck positions.